Along with the popularization of personal computers and workstations, desktop publishing (DTP) systems and computer-aided design (CAD) system have prevailed. Under such circumstance, a color reproduction technique that reproduces colors expressed on a computer monitor on a recording sheet using color agents has acquired much importance. For example, in DTP using a computer system having a color monitor and color printer, after a color image is created, edited and processed on the monitor, it is output using the color printer.
The user of such system strongly desires perceptual matching between the image on the monitor and the output from the printer. However, attaining perceptual matching between the image on the monitor and that of the printer comes with difficulty for the following reasons.
The monitor expresses a color image by emitting light components of specific wavelengths using a phosphor and the like. On the other hand, the printer expresses a color image by reflected light components that remain after light components of specific wavelengths are absorbed using inks and the like. Since the monitor and printer have such different image visualization forms, they have large different color reproduction ranges. Furthermore, even within the monitor, a liquid crystal system, a CRT system using electron guns, and a plasma system have different color reproduction ranges. Also, the color reproduction range of a single printer varies depending on paper qualities and inks or toners, and amounts of inks or toners used.
In order to attain perceptual matching between images on media having different color reproduction ranges, various gamut mapping processes that define correspondence between two different color reproduction ranges in a uniform colorimetric system are available. The qualities of such gamut mapping processes are ultimately determined by subjective evaluation for various images. However, subjective evaluation requires huge cost, and it is difficult to reflect the evaluation results upon gamut mapping processes.
Hence, analysis and evaluation techniques for a gamut mapping process, which can determine quality and can reflect the determination result upon the gamut mapping process, are needed.
Some analysis techniques for determining the quality of a gamut mapping process use quantitative evaluation scales (e.g., calculations of the total sum of color differences in all colors, evaluation of color differences of individual colors, and the like). However, an image is a combination of color information and space information, and the quality of a gamut mapping process must be determined in consideration of whether or not space information is reasonably preserved. The aforementioned quantitative evaluation scales do not contain any determination factors for space information and, hence, only one aspect of the gamut mapping process can be evaluated. Furthermore, since color information is distributed in a three-dimensional space, quantitative evaluation information can be quite large, and desired local information can be hard to find.